The mood in the Conservative party on Thursday night will be determined at least as much by how well Ukip does in the local elections as by how badly the Tories do. Losses to Labour in the hundreds are expected, given where the two parties start these elections from. But it is the smaller number of seats that Ukip seems likely to win that will have a disproportionate impact on the Conservative psyche.

Many in the party have for some time been preoccupied with how to combat the threat of Ukip. But that preoccupation has become an obsession since David Cameron's speech on Britain's relations with Europe and his promise of an "in-out" referendum failed to dent Ukip's appeal. A strong Ukip candidate and a campaign that denied the Conservatives a morale-boosting gain in the Eastleigh byelection added to the pressure. If Ukip adds sizeably to its number of county councillors on Thursday, it will do more than rub salt in Tory wounds; it will start another round of soul-searching over what to do about Ukip.

The Tories should start by putting the challenge posed by the party into perspective. The Ukip challenge is not, first and foremost, a problem about Europe. As Michael Ashcroft pointed out earlier this week, if Nigel Farage's primary aim really is to withdraw Britain from the EU, then taking votes away from the one party prepared to offer that option after the next election is a funny way of achieving it. Polls show that it is not the Europe issue – or indeed any policies at all – that drive voters to Ukip.

The heart of the party's appeal is that it prefers life as it once was in Britain to what it is today. It is this emotional basis that makes dealing with Ukip in government so difficult. The problem is that there is an irreducible core of voters in Britain who simply regard as being beneath contempt the compromises made by any administration as a result of the law, or international obligations or (for now) a coalition agreement.

These people have seen their lives and what they can expect for themselves and their families change for the worse in recent years. When Cameron talks about the global race – the opportunities that lie ahead for Britain and the risks of being left behind – these people look at their very personal race, and fear it has already been run. They feel they have been abandoned by all political parties. It is no accident that Ukip does disproportionately well among older, non-graduate, white men.

The ranks of these disaffected voters have been swelled not only by concerns over immigration and migration during the recession, but also by what they see as the failure of the political system to deal with everything from the row over MPs' expenses and the rise of the "something for nothing society" to the banking crisis and flagrancy of bonus culture.

Cameron has to take note of these frustrations, but he also has to distinguish between those who are impatient with his lack of progress as prime minister and those who are voting Ukip as a premeditated act to put themselves beyond the reach of mainstream politics.

In other words, he has to address those who are willing to take yes for an answer and find practical ways of demonstrating how the future can be better and fairer, rather than get trapped into making empty promises about returning to a past which probably never existed.

The Tory strategy must be about pitching a big tent rather than trying to huddle for warmth inside an ever smaller one; given the electoral arithmetic, Cameron doesn't have the luxury of choosing between those who've defected from the Tories to Ukip since 2010 or pro-coalition voters who supported the Lib Dems at the last election.

Cameron needs both and more besides to win next time. That means offering a clear vision of what Britain will look like when it emerges from austerity, who he wants to see sharing in what he used to call the "proceeds of growth" and reassurance that the rewards of recovery will be shared fairly. Above all, he has to stick to his guns, particularly after nights like tomorrow that will be bad for the Conservatives and good for Ukip. To stand any chance of winning in May 2015, Cameron has to make clear now that there can be no turning back.